Transition from Steady to Oscillatory Flow Natural Convection of Low-Pr Fluids in 3D Bridgman Configuration for Crystal Growth

A numerical study of the transition from steady to oscillatory flow natural convection of low- Prandtl number fluids inside the 3D Bridgman configuration has been carried out. The three-dimensional Navier-Stokes and energy equations, with the Boussinesq approximation have been discretized by means of a finite volume procedure which employs a second order accurate central difference scheme to treat diffusive and convective fluxes. In natural convection, the buoyancy force is only driving the flow and its intensity can be move a harmful effect on the crystal growth, such as the striation. Naturally, the steady state flow is obtained for low Rayleigh number and shows a great dependence between the Rayleigh number, the flow structure and the heat transfer rate. A low increase in the Rayleigh number we guide to determine the critical point in which the 3D flow became oscillatory. This regime appears by a sinusoidal signal in the time and developed in each period of time

Combination between the Inclinations of the Enclosure and the Magnetic Field Orientation on the Oscillatory Natural Convection

In this paper, we study the combination between the inclinations of the enclosure and the magnetic field orientation on the oscillatory natural convection. For this, a cylindrical enclosure filled with electrically conducting fluid, has an aspect ratio equal to 2, and subjected to a vertical temperature gradient and different uniform magnetic field orientations were considered. The finite volume method is used to discretize the equations of continuity, momentum and energy. Our computer program based on the SIMPLER Algorithm has a good agreement with available experimental and numerical results. The time-dependent flow and temperature field are presented in oscillatory state, for different cases: inclination of the cylinder, under the effect of magnetic field in different orientations (δ = 0°, 30°, 45° and 90°) and the combination between them. The results are presented at various inclinations of the cylinder (φ = 0°, 30° and 45°), and the Hartmann numbers Ha ≤ 50. The stability diagrams of the dependence between the complicated situations with the value of the critical Grashof number Grcr and corresponding frequency Frcr, are established according to the numerical results of this investigation. The combination between the studied state has a significant effect on the stabilization of the convective flow, and shows that the best stabilization of oscillatory natural convection is obtained at the inclination of the cylinder φ = 30°, and the applied of radial magnetic field (δ = 0°)

Cyanobacterial bloom mitigation using proteins with high isoelectric point and chitosan-modified soil

A new environmental friendly method was developed for cyanobacterial blooms mitigation using local lake shore soil modified by protein with high isoelectric point (pI) and chitosan jointly. Results suggested that 5 mg/L lysozyme (pI ≈ 11) and 100 mg/L bromelain (pI ≈ 9.5) modified 10 mg/L soil can both reduce the surface charge of microcystis aeruginosa, the dominant species forming cyanobacterial blooms, from -26 mv to -10 mv and remove 73% and 60% of algal cells in 30 min, respectively. The limited improvement of removal efficiency was due to the small flocs (< 60 μm) formed by charge neutralization, which need more than 90 min to settle in static condition. However, when the small flocs were linked and bridged by the other modifier, chitosan with long polymer chain, large flocs of about 800 μm and 300 μm were fomed and more than 80% of algal cells were removed in 5 min and 30 min by lysozyme-chitosan modified soil and bromelain-chitosan modified soil, respectively. The lower removal ability of bromelain-modified soil was due to the lower charge density leading to less powerful in destabilization of algal cells. Depending on the bi-component modification mechanism including charge neutralization of proteins with high pI and netting and bridging function of chitosan with long polymer chain, it is possible to flocculate cyanobacterial blooms in natural waters effectively using locally available materials

3D Numerical Simulation of Turbulent Mixed Convection in a Cubical Cavity Containing a Hot Block

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